Let's Talk About Multiple Sclerosis (MS) Causes
Spoiler alert: Nobody really knows the exact cause of multiple sclerosis, and honestly, there are likely many.
Even though doctors know more than ever about multiple sclerosis (MS), they still haven't been able to pinpoint the true cause. What is for sure? It’s definitely not your fault you have the autoimmune condition, and there is probably nothing you could have done to predict or prevent it. But there is plenty you can do now to live a healthy and fulfilling life with MS. More good news? Scientists are gaining insight about this condition every single day. And, while the root of its cause may still baffle those who study it, they do know how disease-modifying treatments (DMTs) and lifestyle changes can help you experience fewer relapses and longer remissions.
Our Pro Panel
We've got the doctor-approved scoop on causes, symptoms, treatments, and a jillion other facts and tips that can make life with MS easier.
Meghan Beier, Ph.D.
Assistant Professor of Physical Medicine and Rehabilitation and Clinical Neuropsychologist
Johns Hopkins Medicine Multiple Sclerosis Center
Bruce Cohen, M.D.
Chief of MS/Neuroimmunology, Department of Neurology
Northwestern University Feinberg School of Medicine
Neeta Garg, M.D.
Associate Professor of Clinical Neurology
University of Miami Miller School of Medicine
There’s no one single cause of MS. Researchers have identified genes, environmental triggers, infections, and more that may play a role in causing MS.
MS isn’t hereditary, but genetics may still play an important role in MS. MS is not passed down from generation to generation, per se, but certain genetic risk factors probably are.
No, multiple sclerosis can’t be passed from person to person. MS is not an infection, but viral infections may play a role in triggering MS. A pair of herpes viruses—HHV-6 and Epstein Barr virus—are two likely suspects.
MS is an autoimmune disease. The immune systems of people with MS mistakenly attack protective myelin that surrounds cells in the central nervous system. This immune response causes inflammation and damage, which leaves behind lesions that can be seen on an MRI.
What Is MS Again?
Multiple sclerosis is an autoimmune disease. That means your immune system mistakenly attacks healthy tissue, causing damaging inflammation. In the case of MS, immune cells target your central nervous system (CNS), and they specifically zero in on the myelin sheath. This fatty tissue protects your nerves and helps them efficiently conduct messages between your brain and body.
So, here's what occurs when MS strikes:
The immune system mistakes myelin for something dangerous, like a virus, a splinter, or a break in the skin.
Immune cells (such as T-cells and others) attack myelin in a misguided attempt to protect you, and the inflammation damages the myelin and sometimes the nerve fibers, too.
Damaged myelin means the nerves can’t transmit electrical impulses like they did before—which means messages get lost or become erratic as nerves try (and fail) to communicate.
Damaged myelin and nerve fibers scar over—"sclerosis” means scarring—causing lesions. These scars can usually be seen on a magnetic resonance imaging (MRI) scan. The symptoms you feel are a direct result of this damage.
So, What Causes MS?
All doctors know for sure is that there are likely many things that cause it. MS is what’s known as a multifactorial condition, which means it's likely that a variety of components combine to trigger that overactive immune response, including:
Family history and genetics
Certain environmental exposures, possibly including infections such as the Epstein-Barr virus, the cause of most cases of mononucleosis in teenagers and young adults
MS risk factors are as varied as MS symptoms, and researchers aren’t sure how these risks might interplay, or which are the strongest ones to consider. What they are sure of is that you’re able to control some factors (like whether or not you smoke, for example) but not others (like if one of your parents had MS).
What's the Role of Genetics in MS?
When it comes to MS, many researchers believe who you are, who your parents are, who their parents were, and from what part of the planet you all originated factors into your overall risk for developing this condition. Let's break down some of those genetic factors now:
People who have a sibling or a parent with MS are more likely to get MS themselves, but strictly speaking, MS is not hereditary. It’s even possible for one identical twin to have MS while the other does not, according to a study published in Nature. If genes completely controlled whether you get MS, both twins would have the disease, which suggests other factors, likely environmental conditions, are also at play. However, scientists do believe that genetic predispositions for developing the disease may be passed along from generation to generation.
In fact, researchers have identified a gene or two that may increase the risk of getting MS. Changes to the gene known as HLA-DRB1, which produces the body’s instructions for making a protein that’s crucial to the immune system, is the strongest genetic predictor of MS that we currently know about.
It’s true: Women are four times more likely to get the most common form of MS (relapsing-remitting MS, or RRMS, for short) than men, according to the National Multiple Sclerosis Society. But why? Does it all come down to hormones, or some other factor specifically associated with being female? Researchers are still investigating this question. One study published in the Journal of Clinical Investigation showed that women produce higher levels of a blood vessel receptor protein, SI PR2, than men do, and the protein is present at even higher levels in the brain areas that MS typically damages. But again, most studies point to multiple factors, including female hormones, Vitamin D levels, inflammation, and even obesity, according to John Hopkins Medicine.
Your ethnic background may also play a role. Caucasians and African-Americans are most at risk for getting MS, but the disease is often more aggressive in people of Asian, African, or Latino descent. Some experts theorize that reduced access to healthcare in minority populations may contribute to delayed diagnosis and treatment, leading to more severe symptoms.
What Role Does the Environment Play in MS?
Multiple studies suggest that early exposure to sunlight, vitamin D levels, and dangerous chemicals found in cigarette smoke can affect your individual MS risk.
For years researchers have studied a possible connection between the Epstein-Barr virus (EBV) and MS. Multiple studies show intriguing associations between the two. For instance, most people with MS test positive for EBV antibodies, leading some experts to believe that prior EBV infection may be a possible cause of MS—while others think that latent EBV can be reactivated by other environmental risk factors (like those listed below) that together lead to MS. And while this common virus is found in 90% to 95% of the population, it tends to be very mild (or even asymptomatic) in children and more severe in teens and adults (and is the main cause of mononucleosis, a.k.a. "the kissing disease"). According to some research, your risk of developing MS more than doubles if you had mono in your teen or adult years.
Some of the environmental contributors to MS make even experts scratch their heads, and one of the most surprising is where you live. If you were to look at a map that had pins representing everyone with multiple sclerosis, you’d see a lot fewer pins around the equator than north or south of it. So, if you’re from the tropics, you have a decreased risk for MS.
Even more interesting is the effect birthplace and travel has on MS risk factors. If you’ve migrated before you’re 15 years old, you take on the risk profile of wherever you moved. If you’ve moved after the age of 15, your risk profile correlates to wherever you were raised before you moved.
Studies also show that a lot of exposure to sunshine during childhood and the teen years lowers your risk of developing MS as an adult. This is likely related to low levels of vitamin D (the very next risk factor listed, so keep reading!), which everyone can directly absorb from sun exposure.
Vitamin D Levels
Possibly related to geography is vitamin D: People who get less of it have a greater risk of MS. Most people get the bulk of their vitamin D from sunlight, since we all absorb it through our skin. (And the tropics get plenty of sunshine.) Additionally, researchers believe there may be a link between adequate vitamin D levels and a healthier immune system, but aren’t sure what the link is. People with a family history of MS or those who live in more temperate climates may want to consider vitamin D supplementation.
Smoking is the number-one preventable risk factor for MS. The rise in MS rates mirrors the rise in smoking rates between 1950 and 2000, according to the World Health Organization. Some research suggests almost half of people who had MS have smoked, and more than 1 in 10 with the disease currently smoke.
Smoking nearly doubles the risk of getting MS. If you already have MS, smoking will make its symptoms worse. Clinically isolated syndrome (CIS) is more likely to progress into relapsing-remitting multiple sclerosis (RRMS) in smokers, and RRMS is more likely to advance to secondary progressive MS (SPMS) at a faster rate in those who continue to light up.
What’s more, MS symptoms strike smokers harder than non-smokers. Smoking damages our bodies, and whole-body damage kicks off a whole-body (systemic) inflammatory response. Harmful inflammation is especially detrimental for people with MS. If you smoke, do everything in your power to quit. If you don’t smoke, don’t start. If you need help, seek resources to stop smoking today.
What Does Obesity Have to Do With MS?
Obesity is a serious public health problem in the U.S. According to some estimates, it’s responsible for more years of life lost than smoking—and that’s saying something. Being obese is associated with cardiovascular disease, type 2 diabetes, some cancers, sleep apnea, and much more. It’s likely that MS is on that list, too.
Obesity in childhood is thought to increase the risk of MS. One German study looked at data from 453 children and adolescents with MS. It showed that kids with obesity are at twice the risk for MS as kids with a normal body weight. They also had more frequent relapses and relapsed more often while on disease-modifying drugs. Other studies suggest obesity is particularly dangerous for girls when it comes to MS risk. Researchers aren’t sure why obesity in girls brings a greater risk factor, but some speculate it may have to do with higher levels of inflammation.
Obesity is known to cause chronic, low-grade inflammation, so it’s likely plays a role in MS risk for obese adults, too. Being seriously overweight also contributes to vitamin D deficiency. To compound matters, researchers believe that people with obesity may get less vitamin D in their diets, and that obesity itself may alter the way the body absorbs and processes the vitamin—a vicious circle.
Can Infections Cause MS?
Remember how in MS the immune system mistakes myelin for an invader and damages it? Well, what if there were an actual invader? The immune system leaps into action to fight off the invader, but never gets the message to back down when the threat is gone, and just keeps attacking. Some clues point to viral infection as a possible trigger of MS.
The strongest suspects are a pair of herpes viruses: human herpesvirus 6 (HHV-6) and Epstein-Barr virus (EBV, a.k.a. human herpesvirus 4).
Although HHV-6 is most closely associated with a rash that affects babies and kids (not the ones that cause oral and genital herpes; those are HSV-1 and HS V-2), these two viruses frequently target the central nervous system. EBV infections are associated with mononucleosis, viral meningitis, and a few chronic autoimmune diseases, including MS.
Researchers know that the risk of MS goes up after an EBV infection, and some think that EBV can activate genes that increase the risk of autoimmune diseases such as MS, according to a study in Nature Genetics.
While these viruses are associated with an increased risk of MS, their role is far from clear. Studying viruses as a cause for MS is tricky. Researchers have to show that the virus was in the body before the disease develops, and they must show that the viral infection triggers MS, not just happens at the same time. Plus, it’s only fair to note that EBV and HHV-6 are very common and a lot of people have been infected by either in their lives, often without knowing it, and the vast majority of these folks never develop MS.
What Does All This Mean for MS Patients?
If there’s one thing predictable about MS, it’s that it’s so unpredictable. To combat a multi-cause disease like MS, you and your medical team will adopt a multi-pronged approach. And there is plenty to feel optimistic about: People with MS have the benefit of 25 years’ worth of massive progress in research and treatment, and every day, dedicated researchers learn more and more about the causes of MS.
Each piece of data they uncover leads to new insight and innovative therapies. In the meantime, increasingly sophisticated drug protocols help keep symptoms under control for thousands of people. It can be empowering to understand the probable causes of MS, absolutely! But once you gain this knowledge, try to look forward, not backward, and claim your very best future.
- MS Risk Factors: Multiple Sclerosis Trust. (2018). “Risk of developing MS” mstrust.org.uk/a-z/risk-developing-ms
- MS in Women: Science Daily. (2014). “Why Is MS More Common in Women? Study Explains Why.” sciencedaily.com/releases/2014/05/140508121247.htm
- MS in Twins: Nature. (2010). “Twin study surveys genome for cause of multiple sclerosis.” nature.com/news/2010/100428/full/4641259a.html
- MS Genes: Genetics Home Reference. (n.d.). “Multiple Sclerosis.” ghr.nlm.nih.gov/condition/multiple-sclerosis#genes
- MS and Minorities: Neurology Clinical Practice. (2015). “Multiple sclerosis in US minority populations.” cp.neurology.org/content/5/2/132
- MS and Vitamin D: Mayo Clinic. (2020). “Vitamin D and MS: Is there any connection?” mayoclinic.org/diseases-conditions/multiple-sclerosis/expert-answers/vitamin-d-and-ms/faq-20058258
- Smoking and MS (1): Cleveland Clinic Mellen Center. (n.d.). “Smoking and Multiple Sclerosis.” my.clevelandclinic.org/-/scassets/files/org/neurological/mellen-center/mca-smoking-and-ms.ashx?la=en
- Smoking and MS (2): National Multiple Sclerosis Society. (2015). “Smoking and MS.” nationalmssociety.org/NationalMSSociety/media/MSNationalFiles/Research/Stroup_T_Smoking_and_MS_20151110.pdf
- World Smoking Rates: World Health Organization. (n.d.). “Cigarette Consumption.” who.int/tobacco/en/atlas8.pdf
- Obesity and Mortality: Cleveland Clinic. (2017). “Cleveland Clinic Study Finds Obesity as Top Cause of Preventable Life-Years Lost.” newsroom.clevelandclinic.org/2017/04/22/cleveland-clinic-study-finds-obesity-top-cause-preventable-life-years-lost/
- Vitamin D and Obesity: Nutrients. (2013). “Vitamin D and Obesity.” ncbi.nlm.nih.gov/pmc/articles/PMC3705328/
- Adolescent Obesity and MS: Neurology. (2013). “Childhood obesity and risk of pediatric multiple sclerosis and clinically isolated syndrome.” n.neurology.org/content/80/6/548.long
- Adolescent Obesity and MS: PLoS One. (2016). “Weighing Evidence from Mendelian Randomization—Early-Life Obesity as a Causal Factor in Multiple Sclerosis?” journals.plos.org/plosmedicine/article?id=info:doi/10.1371/journal.pmed.1002054
- Obesity and Inflammation: Archives of Medical Science. (2017.) “Obesity and inflammation: the linking mechanism and the complications.” ncbi.nlm.nih.gov/pmc/articles/PMC5507106/
- Viral Triggers of MS: National Multiple Sclerosis Society (n.d.) “Viruses.” nationalmssociety.org/What-is-MS/What-Causes-MS/Viruses
- Epstein-Barr Virus and MS Risk: Nature. (2018.) “Transcription factors operate across disease loci, with EBNA2 implicated in autoimmunity.” nature.com/articles/s41588-018-0102-3